In modern motor vehicles with self-ignition internal combustion engines, continued tightening of exhaust emissions limits means that nitrogen oxides (NOx), among other constituents of the exhaust stream, must be reduced. One method employed for this purpose is catalytic reduction (“SCR method=Selective Catalytic Reduction”) by means of an NOx reduction catalyst. In the course of this exhaust gas aftertreatment, a reduction agent is delivered with the aid of a pump from a storage reservoir to a dosing module, which is located in the region of the exhaust section of the internal combustion engine. By means of the dosing module, a precisely defined quantity of the reduction agent is fed intermittently into the exhaust stream upstream of the NOx reduction catalyst. A urea-water solution (“AdBlue®”) is generally used as a reduction agent.
In order to be able to position the dosing module as close as possible to the exhaust stream, the lower section of the dosing module with the reduction agent injection nozzle situated therein is actively cooled. This ensures that a temperature of 120° C. is not exceeded in the region of the injection nozzle, even if the dosing module is arranged close to the exhaust gas. One disadvantage of this embodiment lies in the lack of cooling to the other subassemblies of the dosing module, in which the actuating magnet for the injection valve is generally arranged and in which the dosing module is connected by means of an electric connection. Owing to the only partial cooling, such a dosing module is not suitable for ambient temperatures of more than 160° C. since otherwise the plug connector and/or the coil of the actuating magnet could suffer permanent damage.
DE 44 36 397 A1 has disclosed a device for the aftertreatment of exhaust gases. In this case, a reduction agent is injected into an exhaust pipe with the aid of a dosing device upstream of a reduction catalyst.
Among the components of the dosing device are a control valve, a dosing valve and a cooling device. The cooling device is embodied as a cooling jacket. This is connected to the cooling water circuit of the internal combustion engine and ensures effective cooling of the dosing device, which is exposed to the high temperatures at the exhaust pipe during operation of a motor vehicle. However, the cooling jacket allows only partial cooling, and, as a result, there may be permanent damage to the electric actuating magnet and/or to the plug connection.
EP 2 192 280 A1 relates to a temperature management system for a dosing device for a urea-water solution in an exhaust system, wherein an injector is cooled. For this purpose, use is made of a cooling liquid taken from the engine cooling circuit. The cooling liquid flows through the injector in coolant ducts. Downstream of the injector, the cooling liquid is fed back into the engine cooling circuit.
DE 101 29 592 A1 discloses a dispensing arrangement for an onboard reduction agent in a motor vehicle. This comprises a housing, in which there is a pump for dispensing reduction agent. In operation, there is a flow of compressed air around the pump, wherein baffles guide the flow of compressed air around the pump. In this arrangement, there is turbulent mixing of the compressed air flow. This occurs in a region directly downstream of the compressed air inlet. As a result, the cooling effect of the compressed air on the components around which it flows is increased and, in addition, temperature control of the reduction agent to be injected is achieved. Active water cooling is not provided in this exhaust gas arrangement.